1. Field of the Invention.
This invention relates in general to earth boring bits of the type used to drill oil and gas wells.
2. Description of the Prior Art.
Commercially available earth boring bits can be generally divided into the rolling cutter bits, having either steel teeth or tungsten carbide inserts, and diamond bits, which utilize either natural diamonds or artifical or man-made diamonds. The artificial diamonds are "polycrystalline," used either individually or as a component of a composite compact or insert on a cemented tungsten carbide substrate. Recently, a new artificial polycrystalline diamond has been developed which is stable at higher temperatures than the previously known polycrystalline diamond.
The diamond earth boring bits can be generally classified as either steel bodied bits or matrix bits. Steel body bits are machined from a steel block and typically have cutting elements which are press-fit into recesses provided in the bit face. The matrix bit is formed by coating a hollow tubular steel mandrel in a castin mold with metal bonded hard material, such as tungsten carbide. The casting mold is of a configuration which will give a bit of the desired form. The cutting elements are typically either polycrystalline diamond compact cutters brazed within a recess provided in the matrix backing or are thermally stable polycrystalline diamond or natural diamond cutters which are cast within recesses provided in the matrix backing.
The single piece bits, whether steel bodied or matrix, typically include a bit body with a tubular bore which communicates with the interior bore of the drill string for circulation of fluids. At least one fluid opening communicates the bit face with the tubular bore for circulating fluid to the bit face to carry off cuttings during drilling. A plurality of fluid courses, sometimes referred to as "void areas" or "junk slots" allow the flow of drilling fluid and formation cuttings from the bit face up the bore hole annulus.
In the past, these void areas or fluid courses have tended to be of uniform width and depth, particularly in the gage region of the bit body and have tended to become packed off by cuttings in certain formations. As a result, the bit penetration rate dropped.